1. Technical Field
The present invention relates to a method of manufacturing a surface acoustic wave device that is obtained by forming in one chip an IC region and a surface acoustic wave element region over a semiconductor substrate, and a surface acoustic wave device.
2. Related Art
Surface acoustic wave elements typified by SAW resonators and SAW filters have excellent features: high frequency, small size, high productivity, etc., and therefore have been widely used in communication fields. In step with recent spread of portable communication apparatuses and the like, strong requirements for size and weight reduction of parts used in high frequency bands have been increasing.
In order to respond to the requirements, a related-art document, J. H. Viseer, IEEE, Ultrasonics Symposium, p. 195-200 (1989) for example, has proposed a surface acoustic wave device in which, instead of using a surface acoustic wave element as a unitary filter, a piezoelectric thin film is deposited over a semiconductor substrate part of which has thereon a high frequency amplifying circuit and the like, to thereby form a SAW filter over the semiconductor substrate.
In such a surface acoustic wave device formed in one chip by horizontally arranging an IC region and a surface acoustic wave element region over a semiconductor substrate, semiconductor elements and wires for connecting the semiconductor elements are disposed in the IC region with an insulating film therebetween. In contrast, only an insulating film is disposed in the surface acoustic wave element region. Accordingly, a step arises between the IC region and surface acoustic wave element region. Typically such surface acoustic wave devices are formed in such a manner that a large number of surface acoustic wave devices lie adjacent to each other on a semiconductor wafer. As the number of stacked layers such as insulating layers increases, the step proceeds over the surface acoustic wave element region with changing to a slope, which problematically precludes ensuring of favorable flatness of the surface of the surface acoustic wave element region. If the flatness of the surface is low, the size accuracy of a surface acoustic wave element cannot be ensured in the fabrication thereof, which deteriorates characteristics of the surface acoustic wave element. In addition, it is expected that unevenness of the surface due to the low flatness leads to variation in film thickness of a formed piezoelectric thin film, which results in the variation in resonant frequency of the surface acoustic wave element. Therefore, in such a surface acoustic wave device, the substrate needs to be flattened prior to forming a surface acoustic wave element. However, there has not been any knowledge of planarizing the surface of a surface acoustic wave element region by employing CMP (Chemical Mechanical Polishing) treatment or the like.